To make the dough: Using a stand mixer with a paddle attachment, combine the flour, yeast, malted milk powder, and butter, mixing until the butter chunks are partly broken up and flattened., In a separate container, stir together the water, vanilla, and salt. With the mixer running on low, add to the flour mixture. Mix until the dough just begins to come together but has lots of visible butter chunks intact., Turn the dough out onto a floured surface and fold it over on itself until it comes together (a bench knife is helpful for this)., Form the dough into a 6" x 14" rectangle and fold it in thirds, lining up the edges tidily to stack on top of each other. Turn the folded dough 90° and roll into a 6" x 14" rectangle., Fold in thirds like a letter again, being particular about having the edges line up. Wrap and refrigerate for 30 minutes., After 30 minutes, repeat the rolling and folding process twice more. Wrap and return to the refrigerator for 45 minutes to 1 hour., To make the filling: Whisk all the ingredients together., To shape the palmiers: Divide the dough in half and return one half to the refrigerator. Sprinkle your work surface with sugar and roll the dough into a 15" x 10" rectangle., Sprinkle the dough with 4 to 5 tablespoons of the filling mixture. Place a piece of parchment over the dough and filling. Gently roll with your rolling pin, to press the filling into the dough., Remove the parchment and, starting with the long edges, roll the two sides toward each other until they meet in the center, like a scroll. Repeat with the remaining dough, wrap the scrolls individually, and refrigerate for at least an hour (or freeze for 20 minutes.), To bake: Preheat the oven to 400°F. Line two baking sheets with parchment., Using unflavored dental floss or a sharp knife, slice each roll into 1/3" pieces and lay the slices, cut side up, on the prepared baking sheets, leaving 1" of space between them. Sprinkle the top of each palmier with 1/2 teaspoon of sugar., Bake the pastries for 9 to 10 minutes, until the sugar on the bottom has begun to brown. Remove them from the oven and turn them over with a spatula. Bake for an additional 5 to 6 minutes, until the sugar is lightly browned on the second side. Watch closely: these go from golden brown to scorched very quickly., Remove the palmiers from the oven and let them cool on a rack. They'll crisp up as they cool., Store palmiers, well wrapped, at room temperature for several days; freeze for longer storage.